1. Field of the Invention
The present invention relates generally to the fields of aerospace physics and physiology. More specifically, the present invention relates to a uni-directional cell stretching device which is capable of mimicking the linear load profiles placed on skeletal muscle within the human body.
2. Description of the Related Art
The physiological responses of the living organism to mechanical loading are numerous and varied. One area of special interest to NASA is the effect of mechanical loading on human muscle tissue, specifically the response of skeletal or cardiac muscle tissue to the removal of mechanical load during space flight and the re-application of mechanical load to these tissues on return to the gravitational field of earth or a distant planet. The use of animal and human models to study the effects of mechanical load/unloading on muscle tissue are useful up to a point, but the basic cellular events involved in microgravity-induced muscle atrophy and re-adaptation to terrestrial gravity need to be studied in isolation from the complex set of load-induced responses generated in the whole organism.
One way of examining microgravity-induced muscle atrophy and re-adaptation to terrestrial gravity is to study purified cultured muscle cells in a mechanically active tissue culture environment designed to mimic physiological loading conditions. By utilizing a system which allows the continuous application of mechanical load to cultured cells, the effects of unloading can also be studied. This can be achieved by loading cells for a set period of time (i.e., 10 days) and then removing that load stimulus so as to study the effects of unloading. Load can then be reapplied to the cells in order to study the re-adaptation response to loading after a period of unloading. Such a system, in conjunction with the use of human muscle cells, has clear modeling potential for studying the effects of microgravity (i.e., unloading) and terrestrial re-adaptation (i.e., return to earth) on the basic cellular processes involved in the response of human muscle tissue to such stimuli, a set of responses which are at this time unclear.
There are several commercial cell stretching systems available currently. All of these systems utilize a deformable culture substratum on which the cells of interest are grown. The culture substratum used is invariably an elastic silicone polymer coated with a physiological extracellular matrix compound to enable cell attachment.
One cell stretching system (Sadoshima et al., 1991) uses a sheet of silicone which is stretched by means of a ratchet/frame assembly attached to one end of the sheet. The whole assembly is immersed in tissue culture medium. This system is capable of producing linear stretch on the growing cells but has several disadvantages surrounding the design. First, to increase the amount ot load on the cells the whole assembly must be removed from the medium container and the frame/ratchet moved; second, removal of the assembly from the medium disturbs the cells and can lead to bacterial or fungal contamination and third, the amount of load placed on the cells is directly proportional to the position of ratchet used and hence load application is step-wise rather than continual.
A second cell stretching system, the Mechanical Cell Stimulator (Vandenburgh, 1988) utilizes a circular deformable membrane on which the cells grow but employs a metal pin to stretch the substratum by way of a linear actuator stepper motor lifting the pin up into the center of the membrane. This device allows a continuous load to be applied to the cells but the type of stretch applied to the cells is both linear and radial, the latter of which is non-physiological load stimulus in the case of skeletal muscle. A second problem with this device is the electromagnetic field generated around the cells by the stepper motor, a potential confounding stimulus on the cells.
A third cell stretching system, namely the Flexercell Strain Unit.TM. (Clarke et al., 1996), uses a similar round configuration for its deformable membrane incorporated into the base of a tissue culture plate except that it is stretched downwards by the application of vacuum to the underside of the membrane. This technique also has the disadvantage of production of non-physiological radial loading. All of the devices listed above have a common problem in that the whole device must be placed inside a tissue culture incubator with associated control units being placed outside the incubator.
The prior art is deficient in the lack of a cell stretching device which is capable of mimicking the unique linear loading profiles placed on a large number of human cells. Further, the prior art is deficient in the lack of real-time viewing of the cellular loading/unloading response of human cells. The present invention fulfills this long-standing need and desire in the art.